Jesse Mulligan was overcome with emotion in an impromptu segment on Three's The Project on Wednesday night, calling out the New Zealand Government's inaction on children being separated from their parents at the US-Mexico border.

The host of The Project described the scenes as "the most shocking story for years and years", and said New Zealand's leaders must not let our relationship with the US get in the way of calling out atrocities.

"Can I say something quickly about the children getting separated on the border in Mexico?" he began. "It's the most shocking story in the world.

"It's time for the New Zealand Government to say something about that. The National Party have come out today to say something about that, so have the Green Party.

"We've heard nothing from Labour. Winston Peters has reluctantly talked about it being concerning.

"But [to] these senior Labour ministers - Twyford, Clark, Robertson - what are you willing to put up with in the world? What are you willing to see and not say anything and protect this so-called relationship with the US?

"What would you put up with before saying anything?"

Mulligan was then interrupted by guest host Steve Wrigley, who said he was "a legend for saying that" - but he wasn't finished.

"Audio of children separated from their parents - the only words we can make out are 'mama' and 'papi' - if you've been separated from your child for just a few seconds, you'll know what that feels like for you and the child.

"New Zealand Government - say something, because if you don't say anything you normalise it. This isn't normal; this is a horrible, horrible thing."

Medical staff and lawyers who have visited the Rio Grande Valley shelters have described playrooms of crying children.

AP reports since the White House announced its zero-tolerance policy in April, more than 2300 children have been taken from their parents at the border, resulting in a new influx of young children requiring government care.